GC/MS Loss of signal over time

Question

Good morning everyone,

I am measuring some 'dirty' samples (flavour products) over a couple of days to measure impurities.

Every day I am creating a new calibration curve and injecting a couple of samples.

I am noticing that every day the signal of my calibration standard is lower than the day before.

My question is what could be causing this loss of signal, and how can i fix it?

Some information:

7890B GC with a 5977B single quad MSD

Max temperature: 240 (20C below column max)

Result for highest standard, in areas:
Day 1 100.000

Day 2 85.000

Day 3 70.000

Thanks in advance,

Koos

gchaplai · Accepted Answer

1) Have you searched for an air leak through either a sniffer or through an air water check on the MS?

If there is a leak somewhere then this would account for your loss of signal.

We have experienced this previously with a leak on the inlet column ferrule, septum, and reducing nut.

2) If you system is leak free, it could be your split vent trap filling, hindering pressure control in the inlet. It may need changing.

3) When was your system last tuned? You maybe experience loss of signal becase of loss of detector sensitivity, especially if the areas are low to begin with (<10'000 counts)

4) Failing this, it could be something as simple as you have a small blockage in your syringe

I have a list of possible areas it could be:

GC Inlet Ferrule

Column

Transferline ferrule

Syringe

HED (High Energy Dynode) horn

HED (High Energy Dynode) power supply

Septum

Standards need replacing

Source

Split Vent Trap

EPC

Empty wash vials

GC Inlet nut

Mass Spec chamber dirty

Gold Seal

Liner

Transferline nut

Mass Spec O-ring

Split Vent Line

GC/MS Loss of signal over time

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